A related art computer simulation technology uses a finite element method to predict a shape of a heating coil, a shape of a cooling jacket, and/or heat treatment conditions such as high-frequency heating conditions and cooling conditions in advance, and also to predict deformation, strain and heat treatment quality of a metal workpiece (see, e.g., JP2010-230331A).
A resistance spot welding is one of the methods for welding a plurality of steel sheets that are placed on top of one another. In the resistance spot welding, the steel sheets are placed on top of one another and held between a pair of electrodes, and electric current is applied between the pair of electrodes in a state in which the steel sheets are pressed in a direction along the electrode rods. The pressure contact portions of the steel sheets are then subjected to resistance heating and melted, and the melted region is then solidified into a lump. This melted and solidified portion is called a nugget (see, e.g., WO2011/013793A1 and WO2014/208747A1).
The related art, e.g., JP2010-230331A cited above, merely discloses a general computer simulation technology, and does not specifically disclose how it can be applied to resistance spot welding.